help

[the killer]

How do i understand topic sentence?

[Tdol]

It's the key sentence for a paragraph. A paragraph will generally deal with one idea, so the topic sentence will try to give the main idea for the whole paragraph. It is often at the start and followed by development, but not always- it could be the concluding sentence.
Try here:
http://www.usingenglish.com/glossary...-sentence.html